Gravimetry Analysis Part-3: Drying or Ignition and Calculation; Sample Question with Solution

STEPS INVOLVES IN GRAVIMETRIC ANALYSIS :-

1. PREPARATION OF SAMPLE SOLUTION
2. PRECIPITATION
3. DIGESTION
4. FILTRATION
5.  WASHING
6. DRYING
7. IGNITION
8. WEIGHT
9. CALCULATION

• Filtration And Washing :-

Take filter paper and filter the supersaturated liquid and ppt.

After filtration washing is done by hot water or electrolytic solution.

Impurity will be removed after washing.

Colloidal precipitation should not washed by using water because it lead to peptization.

• Drying or Ignition :-

After drying or Ignition, we can get exactly known structure of the Analyte.

•  Weight :-

Accurately and precisely by using sensitive and modern analytical balance.

•  Calculation :-

Gravimetric factor (GF) :- the weight of analyte per unit weight of precipitation.

GF = wt. of analyte / wt. of precipitation × a/b ( Mol. analyte / Mol. Precipitation)

% of analyte = wt.of ppt × gravimetric factor × 100 / wt. Of sample

Q. A 10.0 ML solution containing Cl¯ was treated with excess AgNO3 to precipitation 0.4368 g of AgCl. What was the conc. of cl¯ in the unknowns ? ( AgCl = 143.321 g/ mol)

Number of moles of Cl¯ = Number of mole of AgCl

= 0.4368/143.321 = 3.048× 10¯³ mol

Concentration of Cl¯ = 3.048 × 10 ¯³/ 0.01

= 0.3048 M

Q2. In an organic sample ( 0.352 g) phosphorus was dissolved and converted to Mg2p2O7 precipitation (0.223 g). Calculation the percentage % P in the original sample ?

Ans. 2P ( gF w 31 g) Mg2p2O7 (gf w 222.6)

GF = 2 ×31/222.6= 0.2738

% Analyte = gram ppt × GF / g.sample ×100)

% p =( 0.223 ×0.2783/0.352×100)

%p = 17.1 %

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